The origin of solar energetic particle events: Coronal acceleration versusshock wave acceleration

We review evidence that led to the view that acceleration at shock waves dr iven by coronal mass ejections (CMEs) is responsible for large particle eve nts detected at 1 AU. It appears that even if the CME bow shock acceleratio n is a possible model for the origin of rather low energy ions, it faces di fficulties on account of the production of ions far above 1 MeV: (i) althou gh shock waves have been demonstrated to accelerate ions to energies of som e MeV nucl(-1) in the interplanetary medium, their ability to achieve relat ivistic energies in the solar environment is unproven; (ii) SEP events prod ucing particle enhancements at energies greater than or equal to 100 MeV ar e also accompanied by flares; those accompanied only by fast CMEs have no p roton signatures above 50 MeV. We emphasize detailed studies of individual high energy particle events which provide strong evidence that time-extende d particle acceleration which occurs in the corona after the impulsive flar e contributes to particle fluxes in space. It appears thus that the CME bow shock scenario has been overvalued and that long lasting coronal energy re lease processes have to be taken into account when searching for the origin of high energy SEP events.